1. Field of the Invention
The present invention relates to a fluid heater and an evaluation equipment incorporating the fluid heater, and more particularly to a fluid heater adapted to precisely respond to changes in flow rate or target supply temperature of fluid and an evaluation equipment provided with the fluid heater.
2. Description of the Related Art
Recently, there is demand for supply of a fluid with conditions such as temperature or flow rate precisely regulated for a development test of a fuel cell, brought to attention as a power supply device to vehicles such as cars, in a biotechnology field, or of a drug. In order to meet the demand, for example, an evaluation equipment provided with a fluid supply means such as a gas supply unit for evaluation tests for a fuel cell as disclosed in the patent document 1 described below has been proposed.
Patent Document 1: JP 2004-273222A
The fluid supply means as disclosed in the patent document 1 evaluates the performance of a fuel cell at a supply temperature of fluid such as oxygen or hydrogen regulated into a desired temperature. Further, the fluid supply means as disclosed in the above-mentioned patent document 1 is employed so as to carry out an evaluation in a biotechnology field or for a development test of drugs, in which a fluid regulated into a desired temperature condition is supplied.
The above-mentioned conventional evaluation equipment has regulated fluid temperature by a heater such as a so-called sheathed heater being positioned within a duct for guiding fluid or a rubber heater wound around the outer periphery of a duct. In these structures, considerable changes of parameters such as fluid supply rate or fluid supply temperature has such problems as causing time lag before fluid heated to a desired temperature is supplied and unexpected failure such as unstable supply temperature of fluid. As a result, the conventional evaluation equipment has such problems that a heating capacity of a heater is not precisely regulated depending on fluid flow rate.
In a structure of a sheathed heater positioned within a duct for guiding fluid, the fluid comes in contact with the heater. Therefore, when combustible fluid or explosive gas such as hydrogen is heated, additional measures for protection against an ignition or an explosion should be taken, resulting in a problem that equipment components are made complicated.
In the case of a rubber heater, there is a problem that electric power cannot be supplied at a high-power density because it is necessary to take into account conditions such as heat resistance limitation of a rubber material wrapping the rubber heater. A structure of a rubber heater wound around a duct, therefore, causes a problem that heat transfer area must be ensured by taking measures to lengthen a duct in which fluid flows, for example. In the case of the rubber heater, there is also a problem that a rubber material on the surface of a duct for electrical insulation has a function of a heat insulating material, resulting in lowering heat transfer efficiency.
Evaluation equipments include the above-mentioned equipment for a fuel cell that requires continuous supply of fluid to an article to be evaluated in one direction, without circulating it. The evaluation equipment cannot take measure to get fluid back to a heater to reheat even if temperature of the fluid heated by means of the heater is far from a desired supply temperature. Therefore, the evaluation equipment with a fluid supply means as disclosed in the patent document 1 or a fluid heater employed therein do not smoothly address the changes in fluid supply temperature or in fluid supply rate. Consequently, an evaluation equipment such as the conventional fuel-cell evaluation equipment or a fluid heater employed therein has such a problem that an evaluation is not carried out with maintaining a high degree of accuracy because of unstable supply of fluid to a fuel cell to be evaluated in trying to carry out an operation test in a simulated state of a fuel cell employed under an environment with sharp load fluctuations or severe temperature fluctuations in use environment such as cars.
Further, in the above-mentioned conventional evaluation equipment, to make fluid supply be widely altered, it is necessarily to make a duct diameter of a fluid passageway large in preparation for supplying a high rate of fluid flow or to employ a heater with a large heating capacity to heat fluid flowing in a fluid passageway. As just described, in the equipment having the duct diameter of the fluid passageway or the heating capacity of the heater be made large, conditions such as fluid supply temperature are well controlled when fluid supply to an article to be evaluated such as a fuel cell is enough large in amount, but are not well controlled when fluid supply is relatively small, resulting in lowered accuracy of the evaluation test.